In its broadest sense, a scientific network is a set of connections between people, places, and things that channel the communication of knowledge, and that substantially determine both its intellectual form and content, and its material and social effects. In practice, such networks can be very personal and intimate, as between close friends and colleagues, or more formal and bureaucratic, joining state institutions and universities, or national and colonial authorities. In the nineteenth-century, letter writing was one of the most important activities for building and maintaining such connections. Darwin's networks extended from his family circle and close friends to readers, observers, and experimenters across the globe, most of whom he never met. His contacts were socially diverse, including women and men from different classes, nationalities, and professions. He extended the social and geographic range of his contacts in large part by tapping into the networks of others, such as Joseph Dalton Hooker and Asa Gray, who were at leading scientific institutions and who carried out extensive administrative correspondence. Other contacts such as William Bernard Tegetmeier and George Frederick Cupples, introduced him to communities of pigeon fanciers and dog breeders.
Bonds of friendship were very important in science in a period when strong institutional structures were largely absent. Darwin had a small circle of scientific friends with whom he shared work openly and who he relied upon to spot weaknesses and to sharpen his thinking. He also looked to this circle for support in times of uncertainty, controversy, or personal loss. Letter writing was not only a means of sustaining such friendships over distance, it was also a medium through which intimacy and trust could be established in the absence of face-to-face contact. His correspondence with Joseph Hooker and Asa Gray illustrates how close personal ties could be built gradually through the exchange of scientific knowledge and the free expression of theoretical differences.
This section contains two sets of letters. The first is between Darwin and his friend Kew botanist J. D. Hooker. The second is between Darwin and Harvard botanist Asa Gray.
Darwin and Hooker
Letter 714 — Darwin, C. R. to Hooker, J. D., [13 or 20 Nov 1843]
Darwin knows Cambridge botanist J. S. Henslow has sent some of Darwin’s South American plants to his friend Kew botanist J. D. Hooker for examination and he is curious about Hooker’s thoughts.
Letter 729 — Darwin, C. R. to Hooker, J. D., [11 Jan 1844]
Darwin begins with an assessment of his views on Hooker. He relates some queries on ratios of species to genera on southern islands, some observations on distribution of Galapagos organisms, South American fossils, and facts he has gathered that led him to conclusion that species are not immutable. He admits to Hooker “it is like confessing a murder”.
Letter 736 — Darwin, C. R. to Hooker, J. D., 23 Feb 
Darwin begins with a charming statement about his friendship with Hooker. He has just completed Volcanic islands and sends queries on Galapagos flora in particular and island floras in general, as well as on the relationship of wide-ranging species to wide-ranging genera.
Darwin and Gray
Letter 1674 — Darwin, C. R. to Gray, Asa, 25 Apr 
Darwin opens by reminding Harvard botanist Asa Gray they met most recently at Kew. Darwin is collecting facts on variation and questions Gray on the alpine flora of the USA. He sends a list of plants from Gray’s Manual of botany  and asks him to append the ranges of the species.
Letter 1685 — Gray, Asa to Darwin, C. R., 22 May 1855
Gray recalled meeting Darwin three years earlier at Hooker’s. Gray has filled up Darwin’s paper [see 1674]. He discusses the distribution and relationships of alpine flora in the USA.
Letter 2125 — Darwin, C. R. to Gray, Asa, 20 July 
Darwin writes a challenging letter to Gray, saying: “But my letter has been horribly egotistical: but your letters always so greatly interest me; & what is more they have in simple truth been of the utmost value to me.” Darwin believes species have arisen, like domestic varieties, with much extinction, and that there are no such things as independently created species. Explains why he believes species of the same genus generally have a common or continuous area; they are actual lineal descendants. Darwin discusses fertilisation in the bud and the insect pollination of papilionaceous flowers. His theory explains why, despite the risk of injury, cross-fertilisation is usual in the animal and vegetable kingdoms, even in hermaphrodites.
This collection of letters between Darwin and Hooker, while Darwin was writing his barnacle books and developing his species theory, provides some insight on their friendship and their approach to information exchange.
Letter 1202 — Darwin, C. R. to Hooker, J. D., 6 Oct 
Darwin catches up on personal matters as well as makes progress with barnacles. He describes “supplemental” males in detail. In working out metamorphosis, their crustacean homologies followed automatically. On the issue of nomenclature reform, Darwin opposes appending first describer’s name to specific name.
Letter 1220 — Hooker, J. D. to Darwin, C. R., 3 Feb 1849
In this gossipy letter, Hooker relates personal matters. Hooker has received Darwin’s earlier letter . He thanks Darwin for saving his correspondence. He sent “a yarn about species” in October mail, and some “puerile” letters printed in Athenæum. He requests Darwin extract anything valuable from his letters to Darwin and Lyell for Athenæum. He mentioned Darwin’s work on complemental males in barnacles is wonderful, but warns Darwin to drop his battle about perpetuity of names in species descriptions.
Letter 1260 — Darwin, C. R. to Hooker, J. D., 12 Oct 1849
Darwin opens by discussing their correspondence. He then moves on to a discussion of the great dam across Yangma valley as a lateral glacial moraine. He reports on the Birmingham BAAS meeting and details of water-cures. He notes that barnacles are becoming tedious; careful description shows slight differences constitute varieties, not species. He ends with a discussion of lamination of gneiss.
Letter 1319 — Hooker, J. D. to Darwin, C. R., 6 & 7 Apr 1850
Hooker apologises for the delay between letters. He says he used to think Darwin “too prone to theoretical considerations about species,” hence was pleased Darwin took up a difficult group like barnacles. Darwin’s theories have progressed but Hooker is not converted. Sikkim has not cleared up his doubts about Darwin’s doctrines. In his second letter he talks about his visit with Falconer.
Letter 1339 — Darwin, C. R. to Hooker, J. D., 13 June 
Darwin writes to Hooker from his water cure in Malvern. He writes on Himalayan stratigraphy. He believes Hooker’s observations of glacial action are the first ever done east of Urals. He also talks about barnacles and the species theory, and he is impressed with variation. Here we see the effect of Darwin’s species sketch on Hooker’s view of willow systematics.
Darwin's close relationship with John Stevens Henslow, the professor of botany at Cambridge, is well known. His letters to Henslow on the Beagle voyage show the young Darwin hard at work trying to impress his Cambridge mentor and establish a degree of independence, while remaining deferential to the elder naturalist. Although Darwin never held a university post, he encouraged and shaped the work of many naturalists, initiating collaborations, offering suggestions for experiments, or inspiring whole research programmes.
This collection of letters documents Henslow’s mentoring while Darwin was on the Beagle voyage and afterwards.
Letter 152 — Darwin, C. R. to Henslow, J. S., 3 Dec 
Darwin expresses confusion on board the Beagle at the definite prospect of sailing. He gives directions for sending mail to Montevideo. He talks of being a sort of Protégé of Henslow’s and it is Henslow’s “bounden duty to lecture me”.
Letter 196 — Henslow, J. S. to Darwin, C. R., 15 & 21 Jan 
Henslow acknowledges receipt of two letters from Darwin and a box of specimens. He mentions attendance at the BAAS meeting and a gift to him of a small living near Oxford, as well as some political news. He congratulates Darwin on the work he has done. The specimens are of great interest and he gives advice on packing, labelling, and future collecting. He suggests that – as a precaution – Darwin sends home a copy of his notes on the specimens.
Letter 249 — Henslow, J. S. to Darwin, C. R., 22 July 1834
Henslow notes that Darwin’s cargo is safe; the fossils have been sent to William Clift. Henslow asks for dried plants (those sent were all of greatest interest). Henslow sends news of Cambridge and mutual friends.
Letter 251 — Darwin, C. R. to Henslow, J. S., 24 July & 28 Oct & 7 Nov 1834
Darwin is excited by Henslow’s high opinion of his collections. He discusses his notes and some new discoveries. He includes a summary of events since leaving Falklands and the geology of Patagonia. The Corallines at Tierra del Fuego convince him of the artificiality of arrangement of their families by Lamarck and Cuvier. The geological expedition in the Andes ends with serious illness and specimens are sent to Henslow.
Letter 272 — Darwin, C. R. to Henslow, J. S., [10–13] Mar 1835
Darwin tells Henslow the termination of the voyage has been decided – September 1836. He writes of the earthquake of Concepción. Given his geological observations (since November), he can now prove both sides of the Andes have recently risen to considerable heights. He writes of his zoological collection and plans to cross the Cordilleras.
Letter 1189 — Darwin, C. R. to Henslow, J. S., 2 July 
Darwin criticises the lecturing system in education and its emphasis on classics. He has forgotten all his classical knowledge. He asks Cambridge botanist J. S Henslow’s help in naming cirripedes, on which he is working. He believes he has made “some very curious points”.
Darwin as Mentor
This section contains two sets of letters between Darwin and two naturalists he mentored. The first is between Darwin and his neighbour, John Lubbock and the second is between Darwin and German naturalist Hermann Müller.
Darwin and Lubbock
Letter 1585 — Darwin, C. R. to Lubbock, John, [Sept 1854]
Darwin sends Lubbock a beetle he cannot identify. He is reading J. O. Westwood [Introduction to the modern classification of insects (1839–40)] and it has reawakened his passion for entomology.
Letter 1720 — Darwin, C. R. to Lubbock, John, 19 [July 1855]
Darwin congratulates Lubbock on finding musk-ox fossil.
Letter 1979 — Darwin, C. R. to Lubbock, John, 27 Oct 
Darwin provides detailed constructive, comments on Lubbock’s paper on Daphnia, [“An account of methods of reproduction in Daphnia and of the structure of the ephippium”, Philos. Trans. R. Soc. Lond. 147 (1857): 79–100].
Darwin and Müller
Letter 5457 — Müller, H. L. H. to Darwin, C. R., 23 Mar 1867
Müller explains how Origin turned him away from a Linnean interpretation of flowers and mosses. He is glad that Darwin appreciates his continuing work on mosses, in support of natural selection, and plans to repeat Darwin’s orchid experiments. He sends an interpretation of the floral anatomy of Lopezia miniata.
Letter 5471 — Darwin, C. R. to Müller, H. L. H., 29 Mar 
Darwin learns that German botanist Fritz Müller is Hermann Müller’s brother.
Letter 5481 — Müller, H. L. H. to Darwin, C. R., 1 Apr 
Müller thanks Darwin for the “Climbing plants” offprint and for references on fertilisation of flowers. Considering the bounty of work already done, he is looking for something original to do. He mentions that Subularia does not grow in Westphalia.
Letter 5657 — Müller, H. L. H. to Darwin, C. R., 23 Oct 1867
Müller thanks Darwin for the German version of Origin  and the portrait. He discusses how dipterous insects are adapted to eating pollen rather than only to sucking nectar. He describes such adaptations in two dipteran species.
Letter 5770 — Müller, H. L. H. to Darwin, C. R., Jan 
Müller thanks Darwin for his photograph and reminding him of Delpino’s work. He intends to start experimenting with mosses to determine which differences in structure are affected by altered conditions of life, and says he would be happy to share his observations.
Darwin worked from a position of considerable wealth and social privilege. He also sought knowledge about plants and animals from persons of very different social station, such as gardeners, artisans, and tradesmen. Darwin's correspondence with the poultry expert William Bernard Tegetmeier and the Scottish gardener John Scott, illustrate how the rigid Victorian boundaries of class could be bridged to a considerable degree by letter writing, while at the same time differences of status were maintained through forms of address and acknowledgement.
Darwin and W. B. Tegetmeier
Letter 1751 — Darwin, C. R. to Tegetmeier, W. B., 31 Aug 
Darwin thanks W. B. Tegetmeier for his offer to supply carcasses of good poultry breeds. He encloses a list [missing] of birds in which he is interested.
Letter 1788 — Darwin, C. R. to Tegetmeier, W. B., [2 Dec 1855]
Darwin raises queries resulting from their meeting and asks a few more favours. Darwin says: “All fish come to my net in regard to variation.” Darwin also notes that he is acquiring pigeons and poultry and he would be particularly grateful for any of the rarer breeds that Tegetmeier could supply.
Letter 3139 — Tegetmeier, W. B. to Darwin, C. R., 4 May 
Tegetmeier sends some replies to Darwin’s queries and data on pigeon flights between Bordeaux and Verviers. He found little use for Brent’s papers. Huxley has asked him to publish in his journal.
The debate about John Scott
Letter 3800 — Scott, John to Darwin, C. R., [11 Nov 1862]
Scottish gardener John Scott notes that Darwin is mistaken in considering Acropera unisexual, with only male flowers [Orchids, pp. 203–10]. Scott has successfully fertilised two A. loddigesii flowers. One is ripening. Dissection of the other shows the pollen accomplishes fertilisation without contacting any stigmatic surface. Abortive ovules found in flowers did not become fertilised when pollinated. Scott suggests Acropera has both unisexual male and hermaphrodite flowers.
Letter 3805 — Darwin, C. R. to Scott, John, 12 Nov 
Darwin thanks Scott for bringing this (see 3800) to his attention and discusses whether or not “male” Acropera bear fruit. Scott's interpretation of Acropera pollination is ingenious. Pollen-tubes of some cleistogamous flowers germinate in the anthers.
Letter 4463 — Scott, John to Darwin, C. R., 14 Apr 
Scott thanks Darwin for his consoling letter. His mind cannot concentrate after losing his position, and he feels “an inward dread of life’s future”. He would have been glad to work for Darwin and understands why Hooker cannot recommend him.
Letter 4468 — Darwin, C. R. to Hooker, J. D., 19 [Apr 1864]
Darwin makes another plea to his friend Kew botanist J. D. Hooker to take Scott on at Kew. Darwin notes that Emma begs him not to employ him at Down. He has just received a long article on the Origin from D. J. Brown, an Edinburgh baker and geologist [see 4464].
Letter 4469 — Hooker, J. D. to Darwin, C. R., 20 Apr 1864
Hooker again refuses to help Scott, citing him as “unfitted” to make his way in the world. Scott is unwilling to take his part in the “struggle for life”, in contrast with Tyndall, Faraday, Huxley, and Lindley, who have established themselves. Scott’s work is not science, but “scientific horticulture”.
Letter 4471 — Darwin, C. R. to Hooker, J. D., 25 Apr 
Darwin thinks his friend Kew botanist J. D. Hooker takes a hard view of Scott’s character, but will not argue further. He turns the conversation to Leersia and his work on homomorphic and heteromorphic crosses in Primula.
Letter 4611 — Darwin, C. R. to Gray, Asa, 13 Sept 
Darwin sends abstract of John Scott’s paper [see 4332] and passes on favourable remarks about Scott. Darwin notes he has finished Climbing plants and is resuming work on Variation. He has received the review of Herbert Spencer but cannot believe Gray wrote it unless he has muddled his brains with metaphysics.
Letter-writing was a space in which women, who were excluded from universities, professional societies, and most specialist journals, could participate in science. Darwin corresponded with a number of women, especially in the field of botany, drawing on their expertise and encouraging their work privately. This collection of letters provides a window into his interaction with scientific women.
Letter 4170 — Becker, Lydia to Darwin, C. R., 18 May 1863
This is a very formal letter written in the third person by Lydia Becker to Darwin. Becker sends flowers of a variety of Lychnis dioica which has bisexual flowers.
Letter 4258 — Becker, Lydia to Darwin, C. R., 31 July 
Becker has found seeds produced by an hermaphroditic Lychnis and will send them. She also discovered some structural obstacles to fertilisation of hermaphrodite Lychnis.
Letter 4260a — Darwin, C. R. to Becker, L. E., 2 Aug 
Darwin thanks Lydia Becker for the Lychnis seed [see 4258], which he will plant in the hope of fertilising the little ovaria. He comments on the two forms of Linum.
Letter 4441 — Becker, Lydia to Darwin, C. R., 30 Mar 1864
Becker sends Darwin a copy of her book [Botany for novices (1864?)], intended to encourage the young, especially ladies, to study nature.
Letter 115 — Darwin, C. R. to Darwin, S. E., [4 Sept 1831]
Darwin writes to his sister Susan. He spent preceding day with Henslow; much had to be done. His friend, Alexander Charles Wood, has written to Capt. FitzRoy about Darwin. Peacock offered the Beagle naturalist appointment first to Leonard Jenyns, who almost accepted, as did Henslow himself. Darwin will talk to Capt. Francis Beaufort [Hydrographer] and FitzRoy. He also sends his thanks to all his family.
Letter 1176 — Darwin, C. R. to Darwin, Emma, [20–1 May 1848]
Darwin writes to his wife Emma. The letter is a combination of personal and scientific matters. He reports on his father’s health, as well as sister Catherine’s and his own. He also notes that Hensleigh [Wedgwood] thinks he has settled the free-will question -– “we have none whatsoever”. He notes that she was right to send the barnacles and gives directions on their care.
Letter 7124 — Darwin, C. R. to Darwin, H. E., [before 17 Feb 1870]
Darwin writes to his daughter Henrietta [Etty]. He sends MS [of chs. 3 and 4, “Comparison of the mental powers of man and the lower animals”, Descent] for her criticism. Darwin fears parts of it are too much like a sermon; “who wd ever have thought I shd turn parson?”
Letter 5585 — Darwin, C. R. to Darwin, H. E., 26 July 
Darwin writes to his daughter Henrietta [Etty]. He prefers not to send her proof-slips of the present chapter [of Variation], which has been enormously altered, but will be glad to have her see slips and revise in the future. He praises her remarks, criticisms, doubts, and corrections.
Letter 5745 — Barber, M. E. to Darwin, C. R., [after Feb 1867]
In this letter, naturalist, artist, and writer Mary Elizabeth Barber replies to Queries on expression based on observations of the Kaffir and Fingoe tribes in South Africa.